1. Field of the Invention
The present invention relates to an optical disk device, and more particularly to a high-definition optical disk device for using grooves and lands for the recording and reproduction of data.
2. Description of Related Art
Optical disks which achieve higher recording densities by recording data on both grooves and lands, rather than on grooves alone, are conventionally known. When data is recorded on both grooves and lands, it is necessary to detect the addresses correctly in both the grooves and the lands. In DVD-RAM systems, a method called CAPA (Complementary Allocated Pit Address) is used in which a particular signal is inserted for each sector irrespective of data recording with regard to time and the signal is reproduced to detect the address. More specifically, each sector includes, at the leading end thereof, an address region (a header portion) independent of a data region, and a plurality of CAPA signals are inserted in this header portion in such a manner that they are offset to left and right with respect to the grooves and lands in the data region. Thus, the address is detected in the grooves and lands using the fact that different CAPA signals are detected between data recording and reproduction with respect to the grooves and data recording and reproduction with respect to the lands.
The above method, however, has a problem in that, because the address region is provided irrespective of the data region with regard to time, the data capacity of an optical disk is decreased accordingly. In addition, the manufacture of such an optical disk is more complicated because the grooves and the CAPA signals are not aligned in a line. There are also problems that the servo systems or the parameter optimal points of servo or the like differ between the data portion and the header portion when recording or reproducing data.
To deal with the above problems, techniques in which wobbles used for storing the address of grooves are used to determine not only the groove address but also the land address have been proposed.
For example, Japanese Patent Laid-Open Publication No. Hei 10-312541 considers the fact that when address information is embedded by recording data 0 and data 1 for a groove which is wobbled in phase at 0 degree and for a groove which is wobbled in phase at 180 degree respectively, the land interposed between these grooves does not necessarily have in-phase wobbles and the address of the land cannot be determined even if these two adjacent grooves have in-phase wobbles, and provides a technique in which two addresses are provided and the address of the land is determined by either one of these addresses.
FIG. 10 shows the address format described in the above-noted publication.
The addresses include region addresses and track addresses (track numbers), and the region addresses are identical for the segments arranged in the same direction. FIG. 10 shows the track addresses only. G1, G2, G3, . . . represent grooves and L1, L2, L3, . . . represent lands. The track number is smaller toward the inner periphery of a disk and increases toward the outer periphery thereof. The track number in G1 is n+1, the track number in G2 is n+2, the track number in L1 is n+1, and the track number in L2 is n+2. Each groove is wobbled, as shown in FIG. 11, and “0” is recorded by in-phase wobbles of 0 degree and “1” is recorded by in-phase wobbles of 180 degree.
With regard to G1, L1, and G2, in a typical situation, because the track numbers are different for G1 and G2, the phase of wobbles formed in G1 and the phase of wobbles formed in G2 are reversed. Consequently, in L1 sandwiched between G1 and G2, the wobble of G1 and the wobble of G2 form phases of 180 degree with respect to each other, namely reverse phases, and the address cannot be detected. To address this problem, in Address 1, an identical track number is assigned to G1 and G2, so that L1 sandwiched between these grooves has in-phase wobbles which can determine the track number n+1. In Address 2, on the other hand, because the original track numbers n+1 and n+2 are assigned to G1 and G2, respectively, the address of L1 provided between these grooves cannot be detected and results in “NG”.
Further, with regard to G2, L2, and G3, in a normal situation, because the track numbers are different for G2 and G3, the phase of wobbles formed in G2 and the phase of wobbles formed in G3 are reversed. Therefore, in L2 sandwiched between G2 and G3, the wobble of G2 and the wobble of G3 form phases of 180 degree with respect to each other, namely reverse phases, and the address cannot be detected. To address this problem, in Address 2, an identical track number is assigned to G2 and G3, so that L2 sandwiched between these grooves has in-phase wobbles which can determine the track number n+2. In this case, in Address 1, the address of L2 cannot be detected and results in “NG”.
It should be noted that, for recording address data on a disk in the form of wobbles, binary data is converted into gray code for recording, gray code being a code wherein, for adjacent binary data, the distance between codes, namely the number of inverted bit, is 1.
FIG. 12 shows a gray code converter 2 for converting binary data to gray code, and FIG. 13 shows a relationship between addresses and gray code strings. The gray code converter 2 includes a plurality of EX-OR (Exclusive OR) gates 1. When an address is 8-bit data, the least significant bit LSB is exclusive ORed with the next higher bit to obtain the least significant bit LSB of gray code. In a similar manner, adjacent address bits are exclusive ORed to obtain gray code. The most significant bit MSB of the address is directly used in gray code. In the exclusive OR operation, two identical inputs result in an output 0 and two different inputs result in an output 1. Accordingly, the binary address data “00000000” is converted to gray code “00000000” for that address. The binary address data “00000001” is converted to gray code “00000001”. The binary address data “00000010” is converted to gray code “00000011”. As is obvious from FIG. 13, the distance between codes for two consecutive address values is always 1.
As described above, conventionally, the land address and the groove address are detected by providing two addresses, Address 1 and Address 2. However, the conventional method merely uses one of these addresses and does not make effective use of redundant addresses. In particular, because there is a possibility that the detected address is erroneous, it is necessary to verify the detected address in some way.
A parity check, for example, is used for error check of detected data. However, the parity check is not desirable because a parity bit must be added to original data and this causes the distance between codes in gray code to exceed 1.